1. Field of the Invention
This invention relates to epoxy resins, and more particularly, diepoxides and reaction products thereof.
2. Description of the Prior Art
Epoxy resins and polyfunctional epoxide compounds have found extensive utility in the field of coating, molding and the like. These polyfunctional epoxides and epoxy resins include the reaction products of dihydric phenols and halohydrins with subsequent dehydrohalogenation to produce epoxides tailored for particular purposes. Undoubtedly, the two types of epoxides which have been found to have the broadest range of properties useful in a plurality of applications are those based upon bisphenol A and epichlorohydrin and those based upon the condensation products of formaldehyde and phenol with subsequent epoxidation with epichlorohydrin. Those epoxy resins which are based upon the epoxidized phenol-formaldehyde condensation products are commonly referred to as novolak resins, and those based upon bisphenol A and epichlorohydrin are known as the Epon.RTM. resins which are manufactured by Shell Chemical Company.
These novolak and Epon resins vary in molecular weight and epoxide equivalent, with these factors being determinative of particular applications for their use.
In most cases, these specific epoxides, even with additional modifications, are limited in one way or another in their applicability to only a narrow range of uses. One determinative factor in selecting an epoxide for a particular use is viscosity. The viscosity of a particular epoxide to a large degree limits the uses to which the epoxide can be made. In the manufacture of coatings, as an example, it is undesirable to use coating formulations which have ranges of viscosity which are either so low that the formulation flows off the surface being coated or so high that it is difficult to apply without the addition of heat and without encountering rheological problems.
Similarly, in applications such as casting, molding or bonding parts and the like, it is desirable to have a relatively low viscosity epoxide which quickly and completely fills mold and interstices. Further, low viscosity formulations are capable of accepting larger amounts of fillers, pigments and the like over higher viscosity epoxies.
Still further, with present environmental constraints upon the use of volatile solvents, it has been a goal in the coating industry to eliminate the use of such solvents and utilize 100 percent solids systems. Such systems are practical when the viscosity of the 100 percent solids systems, i.e. in this instance the epoxy resin, is relatively low.
When epoxy resins are used in molding, casting and the like where thick masses of cured epoxy resin or polyfunctional epoxide are produced, it is necessary to have a 100 percent non-volatile content in the resin or polyepoxide since it is difficult for solvents and the like to be released from the mass during curing, which often results in voids within the mass which are undesirable. Likewise, when epoxies are used for bonding parts as thermoset adhesives, it is desirable to have a 100 percent reactive system without the addition of solvents.
Although many polyepoxides and epoxy resins have been synthesized from various starting materials resulting in aliphatic, alicyclic and phenolic polyepoxides and epoxy resins, by far the most widely used epoxides on a commercial basis have been the Epon and novolak type resins due to their cost and final physical properties for particular applications.
The primary disadvantages of these Epon and novolak type resins are that they have high viscosities relative to molecular weight and require diluents or environmental modifications during application, such as heat and the like, to be used for particular applications.
In order to alleviate this disadvantage, workers in the art have provided reactive diluents such as low molecular weight mono- and polyepoxides which act as a viscosity reducer for the phenolic-based epoxy resins and which react within the system to form 100 percent solids coating and molding resins.
In many instances, these low viscosity diluents are formed by the peroxidation of ethylenically unsaturated materials. Further, other low viscosity epoxides have been produced by the epoxidation of alcohols, diols and polyols with epichlorohydrin.
Exemplary of various epoxy resins and polyepoxides which have been used as reactive diluents and also as reactive compositions alone are those disclosed in U.S. Pat. Nos. 2,925,403; 3,444,111; 3,470,110; 3,477,990; 3,547,881; 3,838,175; 4,119,593; 3,138,618; 3,033,820 and 3,379,653. Most of these epoxides which are of low viscosity and having been used as diluents are the alicyclic epoxides which are formed by the peroxidation of cycloalkenes.
While it is recognized that the epoxy group can be catalyzed and is reactive with amines, carboxylic acids, Lewis acids and the like, different epoxides function differently in these environments. For example, it is recognized that the phenolic-based epoxides are more highly reactive with amines and quaternary ammonium salts than are the alicyclic epoxides, whereas the alicyclic epoxides are more reactive with Lewis acids and carboxylic acids than the phenolic epoxides.
Thus, when a low molecular weight functional epoxide is used as a reactive diluent with a phenolic epoxide, there may be difficulty in obtaining a complete reaction among the epoxides in the composition because of the difference in catalysis and crosslinking rate.
In accordance with the present invention, a low molecular weight diepoxide is provided which is useful as the sole epoxy constituent in forming coatings, moldings and the like and is further useful as a reactive diluent for phenolic epoxides. In addition, the difunctional epoxide in accordance with the invention, when copolymerized with phenolic compounds upon which epoxy resins are normally based, is effective in reducing the viscosity of the final epoxy resins while not deteriorating and sometimes enhancing the final properties of the product to be formed.